Field of the Application
The present application relates generally to surveys of wellbores, and more particularly, to gyrocompassing surveys and measurements taken during the drilling process for wellbores for oil field and gas field exploration and development.
Description of the Related Art
A survey tool configured to be used a wellbore can comprise at least one gyroscopic sensor configured to provide at least one data signal indicative of the orientation of the survey tool relative to the rotation axis of the Earth. For example, the at least one gyroscopic sensor can comprise a rate gyroscope (e.g., a spinning gyroscope, typically with the spin axis substantially parallel to the wellbore). The rate gyroscope undergoes precession as a consequence of the Earth's rotation. The rate gyroscope is configured to detect the components of this precession and to generate at least one corresponding data signal indicative of the orientation of the rate gyroscope's spin axis relative to the Earth's axis of rotation. By measuring this orientation relative to the Earth's axis of rotation, the rate gyroscope can determine the orientation of the survey tool relative to true north. Such rate gyroscopes can be used in a gyrocompass mode while the survey tool is relatively stationary. In certain systems, the survey tool (e.g., a measurement-while-drilling or MWD survey tool) can be part of a steerable drilling tool, and can be used in a gyrosteering mode while drilling is progressing.